Internal combustion engines are controlled in many different ways to provide acceptable driving comfort during all operating conditions. Some methods use engine output, or torque, control where the actual engine torque is controlled to a desired engine torque through an output adjusting device, such as with an electronic throttle, ignition timing, or various other devices.
Under some conditions, there is the potential for poor driveability when the vehicle operator releases and subsequently engages the accelerator pedal. Specifically, as described in U.S. Pat. No. 6,266,597, transmission or driveline gear lash crossing during such conditions can degrade driver feel. For example, when the engine transitions from exerting a positive torque to exerting a negative torque (or being driven), the gears in the transmission or driveline separate at the zero torque transition point. Then, after passing through the zero torque point, the gears again make contact to transfer torque. This series of events produces an impact, which if transmitted to the driver is called clunk, resulting in poor driveability and customer dissatisfaction.
This disadvantage of the prior art is exacerbated when the operator returns the accelerator pedal to a depressed position, indicating a desire for increased engine torque. In this situation, the zero torque transition point must again be traversed. However, in this situation, the engine is producing a larger amount of torque than during deceleration because the driver is requesting acceleration. Thus, another, more severe, impact is generally experienced due to the transmission or driveline lash during the zero torque transition.
As such, in U.S. Pat. No. 6,910,990, the system controls engine torque to transition through the transmission or driveline lash zone by limiting a rate of torque increase during such conditions. In other words, when near the transmission lash zone, engine torque is adjusted at a predetermined rate until the system passes through the transmission lash zone. Further, the limiting may be adjustable based on operating conditions. By varying the limitation on the torque change in this way, driveability can be improved.
However, the inventors herein have recognized a disadvantage with such an approach. In particular, while rate limiting torque changes may reduce clunk, it may also increase a response delay to the point noticeable by the driver. Further, the greater the reduction in clunk (i.e., the more torque increases or decreases are limited), the greater the response delay.
The above disadvantages may be overcome by a vehicle control method for a vehicle having an internal combustion engine coupled to a transmission, the transmission coupled to wheels on a road. This transmission may be an automatic transmission with a torque converter with a torque converter bypass clutch, the torque converter having an input speed and an output speed, the torque converter coupled to a gearbox. This automatic transmission converter bypass clutch may be at minimal capacity (“open converter”), being modulated to maintain a targeted level of clutch slip or capacity or it may be at full capacity (“hard locked”). The method comprising of in response to a driver tip-out during at least some conditions, decreasing powertrain output so that positive torque is not transmitted to the wheels, and after said tip-out and in response to a driver tip-in, and at least during transitioning to transmission of positive powertrain torque to the wheels, retarding ignition timing while adjusting engine airflow until driveline torque has transitioned to the positive side of lash, and then advancing spark angle to rapidly provide output torque.
In this way, it may be possible to coordinate multiple torque actuators during a driver tip-in to both reduce clunk without substantially increasing total response time. For example, by coordinating throttle and ignition timing adjustments during a driver tip-in in this way, it is possible to, in effect, increase pre-charging of the intake manifold and cylinders with airflow so that once the transition through the lash zone is complete, a more rapid torque increase is possible.